I'm using battle scribe and can put in things like conversion beamers/autocannon dreadnoughts/plas-las razorbacks/etc. but none of this stuff is in the Space Marine Codex. Can I actually use this stuff and is there penalties for doing so?

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A stiff chill came over the realm. The occupants could sense something approaching, something bad. They knew the all-devouring had arrived. The ground shook from its excessive mass, the beast clawing at the entrance. In an instant the doors were open and the beast swarmed through. It consumed everything in its path, its claws ripping apart its prey like a lion on an antelope. Within 10 minutes I had eaten all the leftovers in the fridge, and I was feeling really sick.

Got it, codex is only for models they sell, index is for everything else and is legal.

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A stiff chill came over the realm. The occupants could sense something approaching, something bad. They knew the all-devouring had arrived. The ground shook from its excessive mass, the beast clawing at the entrance. In an instant the doors were open and the beast swarmed through. It consumed everything in its path, its claws ripping apart its prey like a lion on an antelope. Within 10 minutes I had eaten all the leftovers in the fridge, and I was feeling really sick.